The present invention relates to an electrical machine comprising a first active part and a second active part, wherein both the first active part and the second active part have a plurality of laminated sub-cores, each of the laminated sub-cores has a plurality of individual laminations, each comprising an axial width, the laminated sub-cores are mutually spaced in an axial direction such that a radial cooling slot is formed between two adjacent laminated sub-cores and the radial cooling slots in the first active part are offset in the axial direction in relation to one another in comparison to the radial cooling slots in the second active part. Furthermore, the present invention relates to a wind turbine with such an electrical machine.
In the present case, interest is focused on electrical machines. Such electrical machines comprise a first and a second active part and/or a stator and a rotor. The active parts can in turn be formed from laminated cores, each having a plurality of individual laminations. The individual laminations are arranged such that radial cooling slots, through which a cooling medium can flow, are produced to guarantee adequate cooling of the electrical machine.
In particular, if the electrical machine is used as a generator in a wind turbine, the operating noises of the electrical machine are of major importance. The noise intensity area surrounding a wind turbine is usually evaluated using a sound pressure level employing the unit dB(A). Thus, there are clear limit values for the sound pressure level depending on the environment and the time of day. For example, in the area surrounding predominantly commercial facilities a limit value of 65 dB(A) must be observed during the day and a limit value of 50 dB(A) at night. In residential areas, in particular in purely residential areas, these limit values are reduced correspondingly. The noise emission of a wind turbine has various causes. Aerodynamic noises, which primarily emanate from the rotor, and a wide range of mechanical noises determine the measured total acoustic power. The various sound sources must be detected and carefully analyzed during development. Each individual cause requires special measures to realize a generally low-noise construction. As a component of the wind turbine, the wind power generator must also comply with the limit values for the sound pressure level specified by the customer. For this reason, not only compliance with the overall level but also with maximum values for individual frequencies or frequency ranges is necessary. If maximum values for individual frequencies or frequency ranges are exceeded, there is talk of individual tones and/or tonalities of the generator.
Hitherto, attempts were made to remedy problems with excessive noise emission by means of measures in the airflow of the cooling circuit and/or the cooling circuits of the electrical machine. Furthermore, the use of corresponding sound absorbing elements of different materials to reduce the noise emissions is known. In the case of synchronous machines, it is also known that the radial cooling slots in the rotor opposite the radial cooling slots in the stator are offset in relation to one another. This has the advantage that a pulsating cooling airflow from the rotor does not directly encounter obstacles in the stator cooling slots and noise emissions are thus reduced.
For this purpose, DE 10 2014 115 666 A1 describes an open induction motor in which a rotor has a structure by means of which air can flow and consequently the cooling efficiency of the rotor and a stator can be improved. The induction motor contains a stator which, having an iron stator core, contains a radial drain hole and a stator coil which is wrapped around the iron stator core. In addition, the induction motor comprises a rotor with a multiplicity of iron rotor cores which are layered in an axial direction of a rotating shaft and are connected to the rotating shaft, and with a rotor coil which is connected to the multiplicity of iron rotor cores. The rotor further comprises channel plates which are layered between the multiplicity of iron rotor cores.
Furthermore, CN 203 278 421 U describes an electrical machine with a stator and a rotor, each having radial cooling channels. The radial cooling slots of the stator and the radial cooling slots of the rotor are offset in relation to one another. Furthermore, it can be provided that the width of the cooling slot in the stator corresponds to half the width of the cooling slot in the rotor. In addition, twice as many cooling slots can be provided in the stator as in the rotor.